Conventionally, two types of devices, namely thermionic and cold cathodes, are known as electron-emitting devices. Known examples of the cold cathodes are surface-conduction emission type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction emission type electron-emitting devices is described in, e.g., M. I. Elinson, "Radio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later. The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, "Thin Solid Films", 9,317 (1972)], an In.sub.2 O.sub.3 /SnO.sub.2 thin film [M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975)], a carbon thin film [Hisashi Araki et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO.sub.2 thin film according to Elinson mentioned above.
FIG. 4 is a plan view showing the surface-conduction emission type electron-emitting device by M. Hartwell et al. Referring to FIG. 4, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 4. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 4 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion. In the above surface-conduction emission type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In forming processing, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenium cones", J. Appl. Phys., 47, 5248 (1976).
FIG. 5 is a sectional view showing the FE type electron-emitting device by C. A. Spindt et al. In FIG. 5, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 5.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32,646 (1961).
FIG. 6 is a sectional view showing a typical example of the MIM type device structure. In FIG. 6, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 .ANG.; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 .ANG.. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathodes can emit electrons at a temperature lower than that for thermionic cathodes, they do not require any heater. The cold cathode has a structure simpler than that of the thermionic cathode and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode is high, while the response speed of the thermionic cathode is low because thermionic cathode operates upon heating by a heater.
For this reason, applications of the cold cathodes have enthusiastically been studied.
Of cold cathodes, the surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the assignee of the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction emission type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the assignee of the present applicant, an image display apparatus using a combination of an surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction emission type electron-emitting device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the assignee of the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat panel display reported by R. Meyer et al. [R. Meyer: "Recent Development on Microtips Display at LETI", Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)]. An application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the assignee of the present applicant.
The present inventors have examined surface-conduction emission type electron-emitting devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned conventional surface-conduction emission type electron-emitting device. Further, the present inventors have made extensive studies on a multi electron-beam source having a large number of surface-conduction emission type electron-emitting devices, and an image display apparatus using this multi electron-beam source.
FIG. 7 is a schematic view showing a multi electron-beam source according to an electrical wiring method examined by the present inventors. That is, a large number of surface-conduction emission type electron-emitting devices are two-dimensionally arranged in a matrix to obtain a multi electron-beam source, as shown in FIG. 7. Referring to FIG. 7, numeral 4001 denotes a surface-conduction emission type electron-emitting device; 4002, a row-direction wiring; and 4003, a column-direction wiring. The row- and column-direction wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 7. This wiring method is called a simple matrix wiring method. For the illustrative convenience, the multi electron-beam source is illustrated in a 6.times.6 matrix, but the size of the matrix is not limited to this. For example, in a multi electron-beam source for an image display apparatus, a number of devices enough to perform a desired image display are arranged and wired.
In a multi electron-beam source in which surface-conduction emission type electron-emitting devices are arranged in a simple matrix, appropriate electrical signals are applied to the row- and column-direction wirings 4002 and 4003 to output a desired electron beam. For example, to drive the surface-conduction emission type electron-emitting devices on an arbitrary row in the matrix, a selection voltage Vs is applied to the column-direction wiring 4002 on the row to be selected, and at the same time, a non-selection voltage Vns is applied to the row-direction wirings 4002 on unselected rows. In synchronism with this, a driving voltage Ve for outputting an electron beam is applied to the column-direction wirings 4003. According to this method, when voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Ve-Vs) is applied to the surface-conduction emission type electron-emitting device on the selected row, and a voltage (Ve-Vns) is applied to the surface-conduction emission type electron-emitting devices on the unselected rows. When the voltages Ve, Vs, and Vns are set to appropriate levels, an electron beam having a desired intensity must be output from only the surface-conduction emission type electron-emitting device on the selected row. When different driving voltages Ve are applied to the respective column-direction wirings, electron beams having different intensities must be output from respective devices on the selected row. Since the surface-conduction emission type electron-emitting device has a high response speed, a time for outputting an electron beam can be changed by changing a time for applying the driving voltage Ve.
A multi electron-beam source obtained by arranging surface-conduction emission type electron-emitting devices in a simple matrix has a variety of applications. For example, when a voltage signal corresponding to image information is appropriately applied, the multi electron-beam source can be applied as an electron source for an image display apparatus.
FIG. 8 is a partially cutaway perspective view of a display panel to which the multi electron-beam source is applied, showing the internal structure of the panel. In FIG. 8, reference numeral 1005 denotes a rear plate; 1006, a side wall; and 1007, a face plate. The rear plate 1005, side wall 1006, and face plate 1007 constitute an airtight container for maintaining the inside of the display panel vacuum. To construct the airtight container, it is necessary to seal-connect the respective parts to obtain sufficient strength and maintain airtight condition. For example, frit glass is applied to junction portions, and sintered at 400 to 500.degree. C. in air or nitrogen atmosphere, thus the parts are seal-connected. A method for exhausting air from the inside of the container will be described later.
The rear plate 1005 has a substrate 1001 fixed thereon, on which n.times.m cold cathode devices 1002 are formed (m, n=positive integer equal to 2 more, properly set in accordance with a desired number of display pixels. For example, in a display apparatus for high-resolution television display, preferably n=3,000 or more, m=1,000 or more. In this prior art, n=3,072 or more, and m=1,024.) Then n.times.m cold cathode devices are arranged in a simple matrix with m row-direction wirings 1003 and n column-direction wirings 1004. The portion constituted by the substrate 1001 to column-direction wirings 1004 will be referred to as a multi electron-beam source.
In this prior art, the substrate 1001 of the multi electron-beam source is fixed to the rear plate 1005 of the airtight container. If, however, the substrate 1001 of the multi electron-beam source has sufficient strength, the substrate 1001 of the multi electron-beam source may also serve as the rear plate of the airtight container.
A fluorescent film 1008 is formed on the lower surface of the face plate 1007. As this prior art concerns a color display apparatus, the fluorescent film 1008 is coated with red (R), green (G), and blue (B) fluorescent substances, i.e., three primary color fluorescent substances used in the CRT field. In FIG. 9A, the respective color fluorescent substances are formed into a striped structure, and black conductive members are provided between the stripes of the fluorescent substances. The purpose of providing the black conductive members is to prevent display color misregistration even if the electron-beam irradiation position is shifted to some extent, to prevent degradation of display contrast by shutting off reflection of external light, to prevent the charge-up of the fluorescent film by the electron beam, and the like. As a material for the black conductive members, graphite is used as a main component, but other materials may be used so long as the above purpose is attained. Further, the fluorescent substances of three primary colors are not limited to the striped layout as shown in FIG. 9A.
The fluorescent substances of three primary colors are formed in a delta layout in FIG. 9B, and may be formed in another layout.
Note that when a monochrome display panel is formed, a single-color fluorescent substance may be applied to the fluorescent film, and the black conductive member may be omitted.
A metal back 1009, which is well-known in the CRT field, is provided on the fluorescent film 1008 on the rear plate side. The purpose of providing the metal back 1009 is to improve the light-utilization ratio by mirror-reflecting part of the light emitted by the fluorescent film 1008, to protect the fluorescent film 1008 from collision with negative ions, to be used as an electrode for applying an electron-beam accelerating voltage, to be used as a conductive path for electrons which excited the fluorescent film 1008, and the like. The metal back 1009 is formed by forming the fluorescent film 1008 on the face plate substrate 1007, smoothing the front surface of the fluorescent film, and depositing Al thereon by vacuum deposition. Note that when fluorescent substances for a low voltage is used for the fluorescent film 1008, the metal back 1009 is not used.
For application of an accelerating voltage or improvement of the conductivity of the fluorescent film, transparent electrodes made of, e.g., ITO may be provided between the face plate substrate 1007 and the fluorescent film 1008.
Dx1 to Dxm, Dy1 to Dyn, and Hv are electric connection terminals for an airtight structure provided to electrically connect the display panel to an electric circuit (not shown). Dx1 to Dxm are electrically connected to the row-direction wirings 1003 of the multi electron-beam source; Dy1 to Dyn, to the column-direction wirings 1004 of the multi electron-beam source; and Hv, to the metal back 1009 of the face plate.
To evacuate the airtight container, after forming the airtight container, an exhaust pipe and vacuum pump (neither is shown) are connected, and the airtight container is evacuated to a vacuum of about 10.sup.-7 Torr. Thereafter, the exhaust pipe is sealed. To maintain the vacuum degree in the airtight container, a getter film (not shown) is formed at a predetermined position in the airtight container immediately before/after sealing. The getter film is a film formed by heating and evaporating a getter material mainly consisting of, e.g., Ba by a heater or RF heating. The suction effect of the getter film maintains a vacuum of 1.times.10.sup.-5 to 1.times.10.sup.-7 Torr in the container.
A voltage corresponding to a video signal is applied to the terminals Dxn and Dyn of the display panel, while a voltage of several kV to several ten kV is applied to the terminal Hv. Then, an electron beam emitted by the multi electron-beam source is accelerated toward the face plate 1007 to irradiate the fluorescent film 1008, which emits light. By sequentially switching devices to be driven, the face plate surface is sequentially scanned to display an image.
However, when the multi electron-beam source is actually connected to a voltage source and driven by this voltage application method, the voltage effectively applied to respective surface-conduction emission type electron-emitting devices varies owing to a voltage drop caused by the wiring resistance.
As the first cause of varying the voltage applied to respective devices, the surface-conduction emission type electron-emitting devices have different wiring lengths, i.e., different wiring resistances in the simple matrix wiring.
Second, the magnitudes of voltage drops caused by the wiring resistances 4004 at the respective portions of the row-direction wiring are nonuniform. This is because a current branches and flows from the row-direction wiring of a selected row to respective surface-conduction emission type electron-emitting devices connected to the row, and thus currents flowing through the respective wiring resistances 4004 become nonuniform.
Third, the magnitude of a voltage drop caused by the wiring resistance changes depending on a driving pattern or a display image pattern in the image display apparatus. This is because a current flowing through the wiring resistance changes depending on the driving pattern.
Due to these causes, if the voltage applied to respective surface-conduction emission type electron-emitting devices varies, the intensity of an electron beam output from each surface-conduction emission type electron-emitting device shifts from a desired value disadvantageously. For example, when surface-conduction emission type electron-emitting devices are applied to an image display apparatus, the luminance of a display image becomes nonuniform or varies depending on the display image pattern.
Variations in voltage become more noticeable for a larger simple matrix size. This limits the number of pixels in the image display apparatus.
The present inventors have enthusiastically studied a different driving method from the above voltage application method.
That is, in driving a multi electron-beam source obtained by arranging surface-conduction emission type electron-emitting devices in a simple matrix, the column-direction wiring is connected not to a voltage source for applying the driving voltage Ve but to a current source for supplying a current necessary to output a desired electron beam. This method pays attention to a strong correlation between a current flowing through the surface-conduction emission type electron-emitting device, i.e., device current If, and an emitted electron beam, i.e., emission current Ie. By controlling the device current If, the emission current Ie is controlled.
The device current If to be flowed through each surface-conduction emission type electron-emitting device is determined with reference to the device current If vs. emission current Ie characteristic, and supplied from the current source connected to the column-direction wiring. More specifically, a driver may be constituted by combining a memory which stores the device current If vs. emission current Ie characteristic, an arithmetic unit for determining the device current If to be flowed, and an electric circuit such as a control power source. The control current source may adopt a circuit form of temporarily converting the device current If to be flowed into a voltage signal and then converting the voltage signal into a current by a voltage-to-current converter.
This method can reduce the influence of a voltage drop caused by the wiring resistance, compared to the above-mentioned method of connecting the voltage source and driving the electron-emitting device. Hence, variations in output electron-beam intensity can be effectively reduced.